Oxidation and corrosion inhibitor for lubricating oils



Patented Mar. 30, 1943 OXIDATION AND CORROSION ITOR FOR LUBRICATING OILS Joseph F. Nelson and Raphael Rosen, Elizabeth, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application July 26, 1939, Serial No. 286,566

20 Claims.

The present invention relates to improvements in types of blending agents charactertistically containing constituents in a state which predisposes blends of these agents with lubricating oils to be corrosive to copper and similar metals. It is concerned particularly with rendering organic sulfide compounds, including polysulflde and hydroxyaryl sulfide anti-oxidants, non-corrosive to copper.

With developments in modern engines toward higher speeds and compression ratios, greater demands are made on lubricating oils for withstanding severe deteriorating conditions. Although well-refined mineral lubricating oils having desirable viscosity characteristics are suitably stable at low temperatures, when exposed to intense heat and oxidation at elevated temperatures in the operation of these modern high-speed engines, they tend to form sludge and varnish-like deposits. For this reason it is desirable to add to the oils substances which prevent such undesirable effects.

Furthermore with increased loads on powerdrive mechanisms and increased adoption of such alloys as copper-lead cadmium-silver, or the like for construction of bearings used in these highspeed engines, critical demands are made also on the lubricants for film-forming qualities and for non-corrosiveness to such metals. For these reasons there has arisen the problem of imparting characteristics of improved oiliness and increased oxidation resistance to the oils. At the same time, the need for preventing corrosion of metal parts of the engines by lubricating compositions has become more acute.

Some definite improvements in the oxidation resistance of lubricating compositions have been made possible by the inclusion of compounds containing one or more non-metallic elements, belonging to the right-hand families of groups and 6 of the periodic table, and which are chemically combined as in phenols, phenolic sulfides, thioamines. and similar types of compounds. In this connection, it has been found that antioxidants have higher effectiveness in stabilizing an oil and preventing corrosion of some metals, such as lead, when they contain sulfur, selenium. or tellurium in a state such that their blends in lubricants fail to pass a copper strip corrosion test.

In attempting to prevent copper strip corrosion by admixing corrosion inhibitors, more is lost than gained if the effectiveness of the sulfur family constituent for improving the oil composition is destroyed or substantially, reduced.

The general method of improving an oxidation inhibiting compound having copper corroding tendencies is carried out in accordance with the present invention by treating the compound with a chemical modifying reactant, preferably in about stoichiometric or even less than stoichiometric proportion to the amount of corrosive component, at an elevated temperature, usually in the range of to 300 C., which is below the temperatures at which either reactant undergoes thermal decomposition. This treatment is continued until the reactants are chemically combined or associated to yield an improved product, a blend of which in a lubricating oil will successfully pass a copper strip corrosion test. No part of the reaction product need be discarded, because the total reaction product serves as an excellent lubricating oil blending agent for inhibiting oxidation and corrosion during the period of service of the lubricating oil in a highspeed' engine.

One type of modifying reactants found particularly effective is an ester of phophorous acid, such as phenyl, benzyl, cresyl, or xylyl phosphites. Similarly, higher homologous aryl, alkaryl, or aralkyl phosphites may be used. An alkyl phosphite prepared from aliphatic alcohols, e. g., ethyl, propyl, butyl, or higher alcohols, may serve in the same capacity. The phosphite radicals also may be partly bound to metal constituents, as in salts. This type of modifying reactant, in removing the copper corroding tendencies from the oxidation inhibitors, leaves them remarkably well improved in color and in oxidation inhibiting action.

A second type of modifying reactants which may be used is a high boiling organic compound containing an unsaturated aliphatic group, which has at least 16 carbon atoms combined with hydrogen in a ratio ranging from about 15 to about 16.7 parts by weight of hydrogen per 100 parts by weight of carbon. For example, the tetramer of isobutene is an aliphatic compound with 16 carbon atoms, which has the maximum designated carbon to hydrogen ratio. Also, high molecular weight, unsaturated aliphatic acids or esters, olefin polymers, and petroleum components containing at least about 16 carbon atoms per molecule and having a ratio of 15 to 16.7 parts by weight of hydrogen to 100 parts by weight of carbon are useful for the present purpose.

Among types of oxidation inhibitors which it is intended to modify in this manner are the phenolic and naphtholic compounds and, especially, their alkylated derivatives, including those which contain various substituents, such as amino groups, said compounds and their alkylated derivatives being preferably associated or combined with a sulfur family element. When sulfur, selenium, or tellurium constituents are absent from their molecules, these phenolic compounds are usually useful for inhibiting oxidation at only lower temperatures. Thus, alkylated phenols, e. g. cresols or higher alkyl phenols, naphthols, e. g. alpha or beta-naphthol, and di-hydroxy phenols, e. g. resorcinol,'and similar substances are able to stabilize hydrocarbon oil at ordinary temperatures, but not very effectively at temperatures in the region above 200 C. Some metal salts of these compounds have greater effectiveness, e. g., phenolates of alkaline earth metals. By combining these compounds with sulfur so as to form their disulfides or polysulfides, their effectiveness for stabilizing oils against oxidation at the temperatures in excess of 200 C. which are encountered in modern engines is improved with attendant reduction of their corrosiveness to alloys such as copper-lead, etc;

In the high-temperature oxidation inhibitors, atoms of the sulfur family metalloid, that is, sulfur, selenium, or tellurium, may be attached directly to the rings of hydroxy aromatic radicals to form a linkage between said rings. ferred to have this linkage join 2 aryl groups containing hydroxyl and alkyl substituents, since such substituents give improved solubility and stability characteristics to the resulting compounds, but other compounds of this same general type may contain a substituted aromatic radical joined through a metalloid linkage to either a similar, substituted aromatic radical, an unsubstituted aromatic radical, or even an alkyl radical, as in the following formula,

wherein R represents an aromatic group which may'contain one or more substituents of the class consisting of hydroxyl, amino, halogen, nitro, and alkyl radicals; R is the same as R, or represents a group which is similar to R, or an aliphatic radical; and S1 represents one or more atoms of a sulfur family metalloid. An excellent specific example of this type of oxidation inhibitor is the compound, di-tertiary-amyl-phenol disulfide, the structure of which may be represented as follows:

OH HO CsHn The substituents may be attached to the rings at other than theindicated positions. In general, these compounds are characterized by containing a metalloid having corrosiveness" to copper as indicated by the copper strip test.

It is pre- Other anti-oxidants have high-temperature, oxidation inhibiting properties and the characteristic of corrosiveness to copper of thecompounds which have just been described. These include aromatic polysulfides, xanthates, thiocarbamates, thioxanthates, xanthogen, polysulfides, thiurams, etc. The following formulae illustrates some compounds of these types:

Still other substances useful as lubricating oil anti-oxidants include sulfurized plant and animal fatty oils and sulfurized hydrocarbon oils, which have had restricted application on account of their corrosiveness to copper.

In order to illustrate the method of improving these oxidation inhibiting compounds by rendering them non-corrosive to copper and the results therefrom, the following examples are presented.

EXAMPLE 1 A mixture of 15.6 g. of di-tertiary-amyl-phenol di-sulfide (C5H11'C6Ha'OI-DrS2, which is black in appearance, and 14.1 g. of trl-cresyl phosphite (mixed in about a 1:1 mole ratio) was heated at to C. for 15 minutes, then, for an additional 15 minutes at to C., whereby a colorless, oily product was obtained.

Specific amounts of the resulting colorless product were added to portions of refined mineral lubricating oils and samples of these blends were tested to observe their action in corrosion tests and to evaluate the oxidation inhibiting properties of the modified di-sultlde inhibitor. Corrosion tests were made on an unblended mineral oil as a blank, on blends of the oil with the antioxidant before and after its modification, and

on a blend of the oil with the unreacted modifying reactant. These tests were conducted under comparable conditions in the following manner and the results are presented in Table 1:

Corrrm STRIP Coxaosron Trsr by discoloration of the copper.

LEAD Touzmmcr: conaosron Tas'r (on Urmsswoon Tnsr) This test is used to determine the tendency of an oil to corrode bearings. 1500 cc. of the oil are maintained at 325 F. andare sprayed for 5 hours against two sets of bearings, one of copperlead and the other of cadmium-silver alloy. The oil dripping from the bearings is recirculated. The bearings are weighed before and after the test to determine any loss inweight. The test is then repeated with addition of a soluble lead compound, preferably lead oleate, to the oil in increments of 0.005%, calculated on the basis of the weight of an equivalent. amount of lead oxide. A loss in weight of 50 mg. or more in the cadmium-silver bearing indicates that the lead tolerance of the oil has been exceeded, and the amount of lead, computed as per cent lead oxide, added in the previous test is recorded as the "lead tolerance." A lead tolerance of below 0.020% is considered unsatisfactory.

Pei 'cent (upper Lead Lubricant composition "twa flzl 333?"? blend test lbO Unblended oil (blank) I 0.00 PnssmL. 0.0l

I 0.125 Failed-.. Uublended ml+di-tertmr -nm l- 25 do 075 phenol disulfide (unmodified). I 50 y 0.125 Passed Unblemled oil+iricrcsyl phosphitc 25 "so." 0. 03

' .50 o lnblended oil+di-tertiaryarnyiphenol disulfide, modified by 125 do treatment with tricresyl phos- Z5 ilo 0.06 phite as in Example I. .50 do It is to be noted that the modified, sulfurcontaining oxidation inhibitor successfully passes the copper strip corrosion test, thereby making its use more practical, whereas the unmodified, dark-colored compound fails to pass. Further, it is to be noted that when the tri-cresyl phosphite is employed alone as a blending agent, the oil blend barely passes the lead tolerance corrosion test, whereas the modified disulfide oxidation inhibitor is substantially as satisfactory as the unmodified disulfide inhibitor even though the disulfide ingredient forms only half the modified product, the other half comprising the tri-cresyl phosphite ingredient.

The relative value of an oxidation inhibitor, before and after its modification, for retarding oxidation of a lubricating oil at high tempera tures is brought out in the following tests, the results of which are presented in Table 2.

Samples were prepared with a refined, light mineral lubricating oil. S. A, E. 20. Blank runs were made on the mineral oil containing no added oxidation inhibitor. Other test samples were blends of the same reference oil with 25% of the oxidation inhibitor before and after it was modified to eliminate its corrosivencss toward copper. These samples were subjected under comparable conditions to the' following test:

()xmxrmx RATE Tl-ZST This consists in measuring the number of cc. of oxygen absorbed by cc. of a lubricating composition sample during minute periods at 200 C.

These data demonstrate that the oxidation inhibiting properties of the modified oxidation inhibitor, which was treated to prevent its corrosion of copper and similar metals, are improved by this treatment. At the same time, the black colored inhibitor was converted into a colorless product,-whichis in itself a useful improvement.

Instead of modifying a high-temperature oxidation inhibitor with only a phosphite to obtain desirable improvements of its corrosion inhibiting and oxidation inhibiting efficacies and color, as demonstrated, it may be modified with the second type of modifying reactant which enables it to reduce sludge formation in the oil, decreases its corrosiveness to copper, and also has beneficial effects on its oxidation inhibiting properties.

Sludge formation is particularly objectionable in lubricating oils subjected to the high temperatures encountered in high-speed engines because the sludge (oil-insoluble precipitate) tends to deposit on hot surfaces of valves, rings, and pistons, thereupon becoming carbonized to harmful hard coatings. The causes of sludge formation are not definitely known, even though sludge formation bears some relation to oxidation susceptibility of oils, for, rather anomalously, many oxidation inhibitors are notorious for increasing sludge formation in well-refined lubricating oils. Since phosphite modifying agents do not, as a general rule, improve anti-oxidants in this respect and have been observed to accentuate sludging, it has been found desirable to' remedy this defect by modifying the anti-oxidants also by the reactants of the second type, which-may be described as being sludge inhibiting modifiers.

The substances especially useful for reaction with anti-oxidants to increase their sludge inhibiting tendencies as well as to reduce their tendencies toward corrosion of copper have, in general, the properties of high molecular weight polymers of iso-olefins, such as tetramers and higher polymers of isobutylene. Polymers of this type are branched, open-chain hydrocarbons containing at least about 16 carbonv atoms per molecule to which are attached hydrogen atoms in a ratio of at least 2 hydrogen atoms to each carbon atoms, as represented in the formula CnHZn. Other synthetic hydrocarbon oils 0btainable by polymerization of cracked wax olefins also supply suitable modifying agents of this type. These substances may even be condensed with a relatively small quantity of cyclic hydrocarbons. The modifying agents should be freefiowing liquids, yet not readily volatile under ordinary conditions. Substances containing more than 15 parts by weight of hydrogen to each parts by weight of carbon and having,

proper qualities to be used as this type of modify ing reactant may be derived from petroleum oil fractions or naturally occuring fatty oils. Unsaturated, higher fatty acids, e. g. oleic acid, their esters and the like, which have hydrogen to carbon ratios above this lower limit may be used in this connection. The heavier modifying reactants of this type are preferably used in smaller proportions than the lower molecular weight reactants.

The following examples illustrate the treatment of oxidation inhibitors with modifying agents which impart improved sludging properties as well as improved corrosion and oxidation inhibiting properties to the inhibitors.

EXAMPLE 2 One-tenth mole of di-tertiary-amyl-phenol disulfide was heated with 0.14 mole of tetraisobutylene for 15 minutes at 230 to 235 C. and then for 20 minutes at 250 to 260 C. The resulting product, when blended with a refined mineral lubricating oil, was found to be noncorrosive in the copper strip test and improved for inhibiting sludge formation.

Using the same procedure with an unsaturated oil, synthesized from cracked wax olefins by comparable results are achieved.

For testing sludging characteristics of the modified oxidation inhibitor, samples prepared by blending 0.2% of the modified inhibitor with .polymerization. in place of tetra-isobutylene,

a light lubricating oil, S. A. E. 20, were subjected to tests carried out in accordance with the procedure described in the Proc. A. S. T. M. 24, 964, II (1924) except for the time. This procedure consists in maintaining g. of the sample in a flask with oxygen at atmospheric pressure at 200 C. for 24 hours, cooling the thus-treated oil,

diluting it with naphtha, then separating the resulting precipitate by filtration after the mixture has stood for one hour at C., and weighing the. precipitate; the milligrams of precipitated sludge are known as theSligh number.

With each 'ofthe blends, a marked reduction of the sligh number was observed as compared with that of the unblendedoil.

The order in which each type of modifying react'ant is used inthe treatment is not of great importance, but it is preferred to limit the proportions of modifying reactants to avoid excessiv diminution in the concentration of the antioxidant. In some instances, it may be preferred to us the sludge inhibiting modifier first to improve the anti-oxidant to some extent, and then lil- Remarkable eflfects er-tn semen of sludge inhibiting modifiers as a class on unblended oils can be illustrated by. results obtained with oleic acid, which isa high molecular weight, unsaturated aliphatic compound containing at least 16 carbon atoms per molecule and having a modifying reactant need be used for each mole of ratio of 15.? parts by weight of hydrogen to 100 parts by weight of carbon. I

Twenty-three. g. of 'di-tertiary-amyl-phenol disulfide were treated with 17 g.-9f oleic acid, CrlHiiaCOOH, at 200 C. for 1 5-minutes. vAt. the end of this period, a blend of the reaction product in a /z% concentration with a S; A. E. 20 refined mineral lubricating oil was found to pass the to complete the treatment with phosphite.

to copper may be due mainly to the presence of free sulfur as an impurity, less than 1 mole of the substance to be modified.

In any event, the phosphite performs the function of improving color and unsaturated aliphatic reactants serve to improve sludging characteristics, while both types of reactants contribute to removal of the corrosiveness to copper and improvement of oxidation inhibiting power of the anti-oxidants.

As previously noted, the reaction products resuit from the union of the modifying reactants copper strip corrosion test. A blend of the unmodified disulfide reactant in only a concentration with the same 011 failed to pass this test. Portions of the modified reactant were tested in blends with a mineral lubricating .oil for oxidation rate and sludging tendency. Using the'same reference oil as described in Example 1, and conducing the tests "under strictly comparable conditions, the following data were obtained:

Table 3 Oxidation rate cc. 0; (10 cc. ag? Lubricant composition of oil) ehm m sol-bed m 15 Unhlended oil (blank) 7440-35 4. 9 Unblended oil+.25% of di-tertiary-amylphenol disulflde modified by treatment with oleic acid as in example 3-- 1642-12 1. 2

Although the phosphite and the sludge inhibiting types of modifying reactants may be used separately, as illustrated in the examples which demonstrate their individual modifying effects, at times it may be more desirable to use a combination of the modifying reactants to obtain a maximum decrease in corrosiveness to copper and an increase in sludge inhibiting-properties For'example, an anti-oxidant is rendered partially non-corrosive to copper by reaction with a phosphite, e. g. tri-phenyl phosphite! tri-cresyl phosphite, or the like, used in a proportion of about or mole to a mole of an anti-oxidant,- such as a disulfide, and is fully modified by further reaction with a fraction of a mole of a sludge-inhibiting modifier, e. g. the olefin polymers, unsaturated fatty acid compounds, and the like.

with the anti-oxidants without splitting 01! any components or constituents. The reaction may be looked upon as an addition reaction, although some rearrangement may occur. I In this respect, thereaction is different from-a condensation reaction, which involves the separation of constituents and in which the-procedure is frequently complicated by'the presence of catalysts and the formation ofundesirable sludges.

For increasing the stability of lubricating oils,

the'modified anti-oxidants of this invention are including those employed in "Diesele'ngines, and may be used with admixtures'goffatty oils. so'ans.

0 agents are useful'in insulatingoils, in highpreb" generally to be-blended therein in concentrations ranging from about ..1 to about 2% by weight. In someinstances, higher concentrations may be preferred, e. g.,' 5% or more. The improved blending agents are effective in many types of petroleum products irrespective of source or method of refining. The colorless product is particularly valuable for us in white oils procured generally by refining parafllnic, naphthenic, or

mixed crude oil fractions of these types to ahigh degree by treatments involving the use of strong mineral acids,je. g., concentrated or fuming sulfurlc acid, clay, solvent extraction, hydrogena tion, aluminumchloride-type compounds, or other reagents and'procedures. Selection of the particular mode of modifying theanti-oxidant may be based on the-particulariuse'of the prodnot. For some purposes, the anti-oxidant is pref-' erably modified to I avoid sludging. Also,-. the modified anti-oxidants may be intermixed or used together with other compounds having.

known oxidation inhibiting action. I

While the present invention is mainlydirectedto improved blending-.agentsfor motor oilsfit'is not limitedentirely to field becausef the'se surelubricants for gears, industrial oils sreases,

etc, They may be used in manyf ,types. d mineral oils which perform lubricating'functio'ns,

of fatty acids or phenols, pour point depressants, V

viscosity improving agents, and other agents used for improving lubricants.

This invention is not to be limited by any theory of reaction or inhibiting activity. The description and examples are illustrative only and any modification or variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claims.

We claim:

1. Process of improving a high-temperature oxidation inhibitor containing a sulfur family element in a state corrosive to copper and similar metals, which consists in reacting said oxidation inhibitor with modifying reactants comprising a phosphite and an unsaturated aliphatic type compound containing at least 16 carbon atoms per molecule with a ratio of about to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon, and heating the mixture to an elevated temperature for a sufficient period of time to form a lubricating oil blending agent which avoids corrosion of copper.

2. A process as described in claim 1 in which said oxidation inhibitor reacted with said modifying reactant is an organic polysulfide.

3. Process of improving a lubricating oil antioxidant of the type containing a corrosive sulfur family metalloid which comprises mixing the anti-oxidant with an unsaturated aliphatic compound having at least about 16 carbon atoms per molecule and a ratio of about 15 to 16.7 parts by weight of hydrogen to each 100 partsby weight of carbon, and heating the mixture at an elevated temperature for a period suificient to decrease the copper corrosion tendency of the anti-oxidant when blended in a refined mineral lubricating oil.

4. A process in accordance with claim 3, in which said unsaturated aliphatic compound is a polymer of an iso-olefin hydrocarbon.

5. A process in accordance with claim 3, in which said unsaturated aliphatic compound is a carboxylic compound.

6. A process of modifying a lubricating oil antioxidant of the type containing a corrosive sulfur family metalloid which comprises reacting the anti-oxidant at an elevated temperature in admixture with an unsaturated aliphatic compound having at least about 16 carbon atoms combined with hydrogen in a ratio of about 15 to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon for a period suflicient to at least partially reduce copper corrosion tendencies of the anti-oxidant, then further heating the resulting product with an admixed phosphite at an elevated temperature to render the product completely non-corrosive to copper.

7. A process for the production of an improved oxidation inhibitor from a hydroxy aryl compound containing a combined metalloid selected from the class consisting of sulfur, selenium, and. tellurium, which comprises heating the hydroxy aryl compound to an elevated temperature in the range of about 100 C. to about 300 C. with an admixed organic compound containing an unsaturated aliphatic group and having at least 16 carbon atoms combined with hydrogen in a ratio of 15 to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon, and maintaining the hydroxy aryl compound at the elevated temperature with a suflicient proportion of said organic compound for a period suflicient to decrease sludging and copper corrosion tendencies when said product is used as an inhibitor in a refined mineral lubricating oil.

8. An improved anti-oxidant composition consisting essentially of ananti-oxidant, containing sulfur corrosive to copper, chemically combined in an addition product with a compound containing a phosphite radical and an organic compound containing an unsaturated aliphatic group and having at least 16 carbon atoms combined with hydrogen in a ratio of 15 to 16.7 parts by weight of hydrogen to each parts by weight of carbon, said composition being non-corrosive to copper when used as an inhibitor in a refined lubricating oil.

9. An improved anti-oxidant composition consisting essentially of an organic sulfide combined in an addition product with a phosphite ester,

said addition product being characterized by being substantially colorless and by being noncorrosive to copper when used as an inhibitor in a refined mineral lubricating oil.

10. An improved anti-oxidant composition consisting essentially of an organic sulfide combined in an addition product with an unsaturated aliphatic compound having at least 16 carbon atoms combined with hydrogen in a ratio of 15 to 16.7 parts by hydrogen to each 100 parts by weight of carbon, said addition product being non-corrosive to copper and decreasing sludging tendencies when used as an inhibitor in a refined mineral lubricating oil.

11. An improved anti-oxidant composition con-'- sisting essentially of a hydroxy aryl disulfide combined in an addition product with a phosphite ester, said addition product being characterized by being substantially colorless and by being non-corrosive to copper when used as an inhibitor in a refined mineral lubricating oil.

12. An improved anti-oxidant composition consisting essentially of a hydroxy aryl disulfide combined in an addition product with an organic compound containing an unsaturated aliphatic group and having at least 16 carbon atoms combined with hydrogen in a ratio of 15 to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon, said addition product being characterized by being non-corrosive to copper and by causing decreased sludging tendencies of the oil when used as an inhibitor in a refined mineral lubricating oil.

13. A composition comprising an oil-soluble chemical reaction product of a hydroxy aryl disulfide and a material selected from-the group consisting of at least partially organic esters of phosphorous acid and high-boiling organic compounds containing an unsaturated aliphatic group and having at least 16 carbon atoms combined with hydrogen in a ratio of about 15 to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon, said reaction product being non-corrosive to copper.

14. A composition comprising an oil-soluble chemical reaction product of a sulfide of an alkylated phenolic compound, and an unsaturated aliphatic compound having at least 16 carbon atoms and containing at least 15 parts by weight of hydrogen to each 100 parts by weight of carbon.

15. A lubricating composition comprising a major proportion of a mineral lubricating oil base stock into which has been incorporated a small amount of a preformed chemical reaction product of an organic sulfur compound and unsaturated aliphatic compounds having at least 16 carbon atoms and containing at least 15 parts by weight of hydrogen to each 100 parts by weight of carbon, said lubricant being substantially noncorrosive to copper.

16. A lubricating composition non-corrosive to copper, comprising a major proportion of mineral lubricating oil base stock into which has been incorporated a small amount of a preformed chemical reaction product of a dialkyl phenol disulfide and an organic phosphite.

17. A lubricating composition non-corrosive to copper, comprising a major proportion of mineral lubricating 011 base stock into which has been incorporated a small amount of a preformed chemical reaction product of a metal salt of an alkyl phenol sulfide and a substance selected from the group consisting of organic phosphites and unsaturated aliphatic compounds having at least 16 carbon atoms and containing at least 15 parts by weight of hydrogen to each 100 parts by weight of carbon.

18.. The method of lubricating bearings containing a metal such as copper, cadmium, silver, and lead, having substantial susceptibility to corrosion by sulfur compounds, which consists in applying to said bearing surfaces a lubricant comprising a major proportion of mineral lubricating oil base stock into which has been incorporated a small amount of a preformed chemical reaction product of a hydroxyl aryl disulflde having oxidation-inhibiting properties but normally corrosive to copper, with an organic phosphite,

said lubricant being non-corrosive to said bearings.

19. A lubricating composition comprising a major proportion of mineral lubricating oil base stock into which has been incorporated not substantially more than 0.25% of a reaction product of a hydroxy aryl disulflde and a material selected from the group consisting of at least partially organic esters of phosphorous acid and highboiling organic compounds containing an unsaturated aliphatic group and having at least 16 carbon atoms combined with hydrogen in a ratio of about to 16.7 parts by weight of hydrogen to each 100 parts by weight of carbon,

said reaction product being non-corrosive to copper.

20; A substantially colorless mineral oil composition comprising a major proportion of a mineral white oil, not more than about 0.25% by weight of a substantially colorless to clear light colored reaction product of a hydroxy aryl disuliide and a material selected from the group consisting of at least partially organic esters of phosphorous acid and high-boiling organic compounds containing an unsaturated aliphatic group, and having at least 16 carbon atoms combined with hydrogen in a ratio of about 15 to 16.! parts by weight of hydrogen to each parts by weight of carbon,- said reaction product being non-corrosive to copper.

JOSEPH F. NELSON. RAPHAEL ROSEN. 

